Fix extend_show parameter name
Fix extend_show parameter name

show operation is an operation to a single object.
The parameter name 'resource_plural' is confusing.

Change-Id: I11e49b3e245e439fc8376ad2052bd59a1fb715d7

rackerlabs/rackspace-python-neutronclient,Juniper/python-neutronclient,noironetworks/python-neutronclient,Juniper/python-neutronclient,openstack/python-neutronclient,huntxu/python-neutronclient,eayunstack/python-neutronclient,rackerlabs/rackspace-python-neutronclient,noironetworks/python-neutronclient,eayunstack/python-neutronclient,openstack/python-neutronclient,huntxu/python-neutronclient